Consider the isothermal section of the A$-$B$-$C ternary alloy phase diagram in Fig. $1.$ Answer the following questions.

$(1)$ Answer the composition of point P$.$

$(2)$ Mark the point where the alloy

containing $30$ mass$\%$ A and $20$ mass$\%$ B in Fig. $1$ on the answer sheet.

$(3)$ Draw a solid line in Fig. $1$ which indicates the compositions with constant concentration C at $40$ mass$\%$ and varying concentrations of A and B$.$

$(4)$ Draw a dotted line which indicates compositions where the concentration ratio of A and B is constant at $3$:$2$ with varying concentration of C$.$

Fig. $1$ Isothermal section of A$-$B$-$C Ternary equilibrium phase diagram